Landslides and Water Management

Monday night we woke up to quite a strong rainstorm. It’s been wet for many weeks already, so we did not think too much of it and went back to sleep. At sunrise we wanted to look around a bit, because we got quite some water (around 150 mm in just a few hours) and to our big astonishment we saw that the area around us was hit by some severe landslides. One of the bigger mudslides had come down the entire mountain at the higher side of our land.

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The picture above gives an idea of the amount of mud that came down, the one below shows the entire path it took. The vertical distance is slightly over 100 meters.

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The mix of mud and trees came to a stop between our two key point dams and the small dam now has an island of mud and tree branches.

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About 20 meters from the house of our neighbors above us another slide came down, but was stopped by some bigger trees just over the fence line on our part of the slope.

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The cause of these two landslides seems not so much instability of the slopes, but human caused concentration of water flow. The big slide is the channel where the water comes down from a mobile phone antenna, a hard surface area of about 1000 square meters. The smaller one is where the rainwater exits the road above to come down the mountain. Because this severe rainstorm followed weeks of rain that already saturated the soil to quite some depth it ended up totally eroding these channels. Once mud gets flowing down these slopes it takes everything down with it.

On the other side of our farm also big parts of the slopes were washed down. These were all steep slopes that didn’t have a lot of stability. Everything on the picture below that is now dark brown was green the day before.

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The landslide on the foreground in the picture above came down over a 100 meters also and crashed on the public road going down the valley.

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With all this rain our water control systems are getting a good test. The terraces look fine:

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We still do not see much runoff, but because the amount of rain is high, we do see water coming up in the lower terraces. Through small streams and channels this excess of water is transported to our valley dam.

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That valley dam was installed a little over two years ago, and with this event it finally filled up to full capacity for the first time. All those springs everywhere though keep adding water to it, so the excess water now has to leave our land as calmly as possible. In the middle on the picture below you can see the overflow of the valley dam.

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When we came here three years ago any severe rain event would create huge flows of water, going down deeply eroded gullies fast to become someone else’s problem on the lands below ours. When the rains ended the flows would quickly dry up. Today all that water flows calmly over terraces and through swales, gets caught in dams and infiltrates the ground. Excess water is slowly released back to the surface and transported away calmly in a process that takes days instead of hours.

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The overflow of the valley dam has been running for over 2 days now and gives a calm constant flow of clear water. We think we did a good job so far with controlling the sometimes excessive rains we experience in the tropics and we look forward to one day finishing the work we still have to do.

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The improvised corral for the pigs got a little wet too, but the piglets are two months old and can handle it. We do need to build a permanent corral soon now, so we can better manage the process of weaning the next group of piglets than we could this time. Lots of work still to do.

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2 Responses to Landslides and Water Management

  1. Pippa says:

    Hey Rene, you left me your website details as part of my MSc research and I came past to visit only to discover that you’ve been dealing with natural hazards over the last week! It’s so great to see that the landslides you mentioned as a site risk in the survey were well managed by your earthworks and water system design. Permaculture proof! Can you do anything to manage that water flow off the top of the hill by the phone tower to further protect your site?
    Best wishes and congratulations on the piglets!

    Pippa

    Like

    • Rene Nijstad says:

      Hi Pippa, thanks for your comment. Ideally we’d ask the owner of the land where the antenna is to reroute the water flow, but with nobody living there it’s a bit difficult to get hold of the right person. Right now it’s a bare channel, so the hazard is worse than it was before. So we’ll stay clear of it for the time being and let all that mud dry out a bit and then we’ll see what has to be done.

      Like

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